A track system is known, wherein the track is essentially U-shaped and adapted for mounting on the mast with the cavity facing the groove. The fastening means are screws being inserted through transverse openings in the track. For fastening the track onto the mast, each individual slide member is to be slid in the groove, until its threaded hole is aligned with the corresponding transverse opening in the track, whereafter a screw is inserted through the transverse opening to engage the threaded hole in the slide member. This is a rather difficult and time-consuming operation, and it is particularly difficult to bring the screw into engagement with the threaded hole. Further, said system has the drawback that the slide member slides downwards, until it abuts the subjacent slide member, if a screw is unscrewed after the track has been mounted. It is not possible to mount this slide member again without loosening all of the remaining slide members which have been used to fasten the track to the mast. This operation is often very time-consuming, since 200 slide members are sometimes used.